Dental crown and method of forming same



Oct. 22, 1940. s. STREIM DENTAL CROWN AND METHOD OF FORMING SAME Filed Oct. 18, 1938 INVENTOR SAMUEL 5T E/M BY I ATTORNEY Patented Oct. 22, 1940 UNITED STATES PATENT OFFICE 2,219,058 DENTAL CROWN ANg) METHOD OF FORMING This invention relates to dental crowns in general and the method of forming the same.

Among the objects of the present invention it is aimed to provide an improved dental crown for 6 a tooth and the method of forming the same, the

size and form of which metal crowns can be accurately predetermined without any danger of injuring the gum line.

It is still another object of the present inven- 1 0 tion to provide an improved form which can be readily made from a stock form and supplemental moldable material and co-operate with the standard casting investment material so that the form can be readily destroyed by heating or the 16 like to produce the mold' cavity.

It is still another object of the present invention to provide an improved method of forming a metal crown for a tooth consisting essentially in measuring the tooth to be restored at the sum 20 line, thereupon selecting a moldable stock form corresponding to the measurement taken, thereupon cutting down the tooth to be restored to the gum line, thereupon fitting the stock form selected with the aid of carding wax or the like down 25 to the gum line, thereupon removing the form so produced with the aid of a stock form and carding wax and attaching a cylindrical projection to this form, thereupon depositing the form so produced in a suitable casting investment material,

30 thereupon removing the form from the investment material by destroying the same with the aid of heat or the like, thereupon pouring the metal, gold or the like, into the mold so produced, and allowing the same to harden, thereupon re- 85 moving the metal crown so produced from the investment material and cutting off all objectionable projections and the like, thereupon locating the crown so produced on the tooth stump previously formed, and finally cementing the 40 metal crown to this tooth stump.

These and other features, capabilities, and advantages of the invention will appear from the subjoined detail description thereof illustrated in the accompanying drawing in which:

Figure 1 is a perspective of the tooth to be restored and the measuring tool associated therewith;

Fig. 2 is a perspective of the measuring instrument after it has been removed from the tooth;

50 Fig. 3 is a perspective showing the tooth to be restored in dash and dot lines, and the stump of the tooth after it had been cut down in full lines;

Fig. 4 is a perspective of a stock form selected 5 with the aid of the measuring instrument;

Fig. 5 is a section of the tooth stump with the stock form initially placed on the same;

Fig. 6 is a perspective of the stock form showing a border portion of carding wax applied thereto; 5

Fig. 7 is a section similar to Fig. 5, showing the stock form re-applied to the tooth stump after the carding wax had been applied, preparatory to final adjustment of the form to the tooth stump; 1

Fig. 8 is a perspective of the form with a cylindrical projection attached thereto;

Fig. 9 is a section of a supply of investment material in a container after the stock form had been burned out and the metal had been poured into the mold cavity formed thereby;

Fig. 10 is a perspective of the metal form removed from the investment material; and

Fig. 11 is a side elevation of the tooth stump with the metal crown in section in finally cemented relation.

In carrying out the method constituting an important part of the present invention, a standard measuring instrument I, is applied to the tooth 2, to be restored or of the tooth to be used as an abutment for a dental bridge with the wire 3, placed at the gum line as illustrated in Fig. 1. The handle 4, in applying the measuring instrument I, is turned in the direction of the arrow 5, until the wire 3, snugly engages the tooth 2, to be restored, at the gum line. Thereupon, see Fig. 2, the wire 3,.js cut at 6, and removed from the tooth 2, and stretched out as shown in Fig. 2 to facilitate measuring the same. With the measurement so obtained, a stock form 1, is selected such as illustrated in Fig. 4. Thereupon this form is fitted in the same way now practiced when fitting a swedged gold shell crown, as an instance the tooth 2, to be restored or to be used as an abutment as aforesaid shown in dash and dot lines in Fig. 3, is ground down somewhat at the occlusal end and then slightly around the sides until the stock form 1 fits snugly over the prepared tooth stump 8, shown in full lines. It is desirable that care be exercised so that the natural tooth is ground down sufficiently to allow for proper and correct occlusion or bite.

Thereupon the stock form I, is positioned on the stump 8, as shown in Fig. 5. If the skirt of the form 1, is too long it of course can be shaved ortrimmed down at the free edge to fit as close to the gum line as possible. If it should be necessary for proper occlusal correction or proper bite, the occlusal or biting surface of the stock form I can be ground down the required extent. In

some instances, it may also be desirable to add Wax to the form I. When the form I has thus -been accurately fitted, the same is carefully removed from the tooth stump 8 and the inner surface that fits over the stump is carefully wiped dry and melted soft inlay wax or carding wax is carefully smeared all around the surface. Care should be exercised that the wax is securely attached to the form I. Thereupon, the form "I is replaced carefully on the tooth stump 8, as shown in Fig. '7, and accurately seated into place, checking to see that the bite is correct. Thereupon with a wax burnisher, wax is carefully applied around the neck of the tooth at the gum line ID to insure an accurate seal and definite seat for v I the finished casting.

Thereupon the form I is removed from the stump 8 and a slight amount of inlay wax is added on the distal or mesial sides or on both the distal and mesial sides as the case may be in order to allow for stoning down and polishing the gold casting to be produced from this form and thus to obtain proper contact points where the cast crown is cemented into position. The form 1 is now ready to be sprued, invested and cast following any of the recognized techniques. As an instance, a short cylindrical stem or projection H is secured to the outer occlusal end of the form 1, see Fig. 8, and thereupon the form I, with this cylindrical stem ll, inserted in a suitable investment material such as the substance l2, in the container or compartment l3, so supported that the free end of the stem H, about emerges or is deposited in alinement with the upper surface 14, of the investment material l2. Thereupon the form I, and its associated stem l I, is removed without disturbing the investment material l2, as an instance by burning out .the form I and stem I I. In order to remove the form I by combustion it is, of course, obvious that its composition should be one that is readily combustible without chemical reaction with the investment material. It is also obvious that the same should be practically free from ash or a combustible residue. To this end, it has been found that good results can be obtained when the form I and stem II are composed of ordinary inlay wax, or an acetate, such as Tenite, or a resin such as Lucite, or the like.

Before the form 1 and stem II have been so removed, preferably a depression I5 is formed around the outer free end of the stem I I, so that when the form I and stem II are burned out, the resulting mold cavity in cross section will resemble the cavity l6 isllustrated in Fig. 9.

Thereupon the cavity I6 so formed is supplied with the metal of which the crown is to be formed. This metal of course should be of a character that can become readily moldable at a comparatively low temperature, such as gold or the like. After the metal has been poured into the mold cavity using the depression l5 as a funnel to facilitate receiving the same and sufficient time has elapsed to permit the same to harden, the metal form I1 is removed from the investment material l2, and will appear substantially as illustrated in Fig. 10. Before this form H can be positioned on the stump 8, the stem l8 and enlargement I9, see Fig. 10, must be first removed and the resulting surface of the form l'l preferably smoothed and polished. Thereupon, the shell I1 resulting, see Fig. 11, may be positioned on the stump 8 and cemented to the stump 8 in the usual way. The intervening space between the stump 8 and shell I! preferably is compactly filled with cement, such as the cement 20.

The resulting cast crown I1 is the ideal and superior type of restoration for the restoring of a posterior tooth either for individual restoration or for an abutment for the construction of a dental bridge.

By means of the use of the special crown form:

1. Time and money can be saved.

2. No tube impression need be taken. This will prevent injury to the free margin of the gum at the neck of the tooth.

3. No bite need be taken. The special crown form is fitted directly in the mouth.

4. No die has to be made.

5. No articulating set up is needed.

6. Little carving-if any, has to be done. Only the necessary changes to allow for proper and correct bite or articulation are required due to the fact that the special crown forms I come already anatomically carved and of approximately correct size.

'7. Because of the even gauge of the special forms 1, twenty-eight gauge for cusps and thirty gauge for the walls a casting of a more even thicknessis obtained and which, of course, means a less bulky crown.

8. Because of the simplicity of the technique required by the method here made possible, it is easy for any dentist to produce a better cast crown both as to fit and carvings than heretofore and with less effort.

9. Because of the recognized advantages of a cast gold crown, because of the simplicity of this technique and because it is a time and money saver in making and producing a gold cast crown, this special crown form should be an aid to the dentist who wishes to make the best type crown restoration with a cast gold crown.

It is obvious that various changes and modifications may be made to the details of construction and to the steps in the method here discussed, without departing from the spirit of the invention set forth in the accompanying claims.

I claim:

1. The method of forming a pattern for the casting mold of a metal crown consisting in accurately measuring the periphery of a natural tooth at the gum line, thereupon selecting a hollow, anatomically simulating, pre-formed stock crown pattern composed of a moldable shape retaining combustible material, volatile and practically free from ash during combustion and corresponding to the measurement obtained, thereupon grinding down the natural tooth in the mouth of the patient and fittingthe stock pattern on the stump of-the natural tooth so formed, thereupon adding soft inlay or carding wax to the inner surface of the stock pattern and replacing the stock pattern on the stump, thereupon accurately seating the stock pattern into place on the stump and conforming the same to correspond to the bite required, and thereupon removing the stock pattern from the stump and smearing inlay wax on the distal and mesial sides to allow for stoning or polishing the casting to be produced preparatory to the casting operation.

2. The method of forming a pattern f r the casting mold of a metal crown consisting in accurately measuring the periphery of a natural tooth at the gum line, thereupon selecting a hollow, anatomically simulating, pre-formed stock crown pattern composed of amoldable shape retaining combustible material, volatile and practically free from ash during combustion and corresponding to the measurement obtained, thereupon grinding down' the natural tooth in the mouth of the patient and fitting the stock pattern on the stump of the natural tooth so formed, thereupon replacing the stock pattern on the stump and conforming the same both as to bite and as to a snug fit on the stump, and finally removing the pattern so reformed ready for the casting operation.

3. The method of forming a pattern for the casting mold of a cast metal dental crown consisting in accurately measuring the periphery of a natural tooth at the gum line, thereupon selecting a hollow, anatomically simulating preformed, stock crown pattern of inlay wax or the like corresponding to the measurement obtained, thereupon grinding down the natural tooth in the mouth of the patient and fitting the stock pattern on the stump of the natural tooth so formed, thereupon replacing the stock pattern on the stump and conforming the same both as to bite and as to snug fit on the stump, and finally removing the pattern so reformed ready for. casting.

4. The method of forming a pattern for the casting mold of a cast metal dental crown consisting in accurately measuring the periphery of a natural tooth at the gum line, thereupon selecting a hollow, anatomically simulating, preformed, stock crown pattern of an acetate such as Tenite or the like corresponding to the measurement obtained, thereupon grinding down the natural tooth in the mouth of the patient and fitting the stock'pattern on the stump of the natural tooth so formed, thereupon replacing the stock pattern on the stump and conforming the same both as to bite and as to snug fit on the stump, and finally removing the pattern so reformed ready for casting.

5. The method of forming a pattern for the casting mold of a cast metal dental crown consisting in accurately measuring the periphery of a natural tooth at the gum line, thereupon selecting a hollow, anatomically simulating, preformed, stock crown pattern of a resin such as Lucite or the like corresponding to the measurement obtained, thereupon grinding down the natural tooth in the mouth of the patient and fitting the stock pattern on the stump of the natural tooth so formed, thereupon replacing the stock pattern on the stump and conforming the same both as to bite and as to snug fit on the stump, and finally removing the pattern so reformed ready for casting.

SAMUEL STREIM. 

